The .alpha.-keto acid ester (also referred to as "oxo acid ester") is of value as an intermediate compound for synthesizing a variety of chemical compounds, and particularly for synthesizing .alpha.-amino acid. Among the .alpha.-keto acid esters, a glyoxylic acid ester prepared from a glycolic acid ester is of great value as a starting compound for preparing a builder of detergent or vanillin or as an intermediate compound for synthesizing pharmaceuticals, agricultural chemicals or polymers.
Heretofore, it has been known that the .alpha.-keto acid ester can be prepared by a gaseous catalytic reaction of .alpha.-hydroxycarboxylic acid ester with molecular oxygen in the presence of a certain catalyst.
U.S. Pat. No. 4,340,748 discloses the use of a catalyst containing at least one of the elements V, Mo, Ag and Cu, and at least one of the elements Sn, Sb, Bi, elements of the first main group, and elements of the second main group, preferably Sn, Sb, Bi, K, Na, Li, Mg, and Ca, for manufacturing a glyoxylic acid ester (which is one of the .alpha.-keto acid ester) by gaseous catalytic reaction of a glycolic acid ester with molecular oxygen. According to our studies, this process is not satisfactory in its productivity, that is, its low rate of production (in terms of space time yield) and its requirement of feed of a large volume of the gas. Further, the Patent suggests that elements of main groups III to V likewise exhibit a catalytic effect. However, no detailed description is given.
Japanese Patent Provisional Publication No. 60(1985) -152442 discloses the use of an expensive silver catalyst for the process of production of glyoxylic acid ester. In the process, the conversion of a glycolic acid ester to a glyoxylic acid ester is ought to be decreased for increasing selectivity to the glyoxylic acid ester. Therefore, the yield of a glyoxylic acid ester is so low as approximately 62% (calculated from about 69% of the conversion of glycolic acid ester and about 89% of the selectivity to glyoxylic acid ester) at the highest.
Japanese Patent Provisional Publication No. 61(1986) -97247 describes a process using a combination of expensive silver and a phosphorus compound (e.g., phosphoric acid, a phosphate such as ammonium dihydrogenphosphate, etc.). The conversion of the glycolic acid ester in this process is as high as 95%. However, the selectivity to the glyoxylic acid ester is as low as about 8%.
The above-mentioned Japanese Patent Provisional Publication No. 61(1986)-97247 further describes a process for the preparation of other .alpha.-keto acid esters such as ethyl pyruvate, methyl phenylglyoxylate and methyl phenylpyruvate using a combination of expensive silver and the phosphorus compound. In this process, it may be a problem that the productivity is low owing to a small feed amount of the starting compound, and the expensive silver is used. Further, in this process, the conversions of the above .alpha.-hydroxycarboxylic acid esters are 99%, 90% and 92%, respectively, and the selectivities are 80%, 86% and 70%, respectively. Accordingly, the yields of the .alpha.-keto acid esters are not satisfactory. Moreover, as described above, it is difficult to obtain the glyoxylic acid ester in a high yield.
Japanese Patent Provisional Publication 2(1990) -91046 describes a process using ferric phosphate supported on an .alpha.-alumina carrier as the catalyst. In this process, the yield of a glyoxylic acid ester which is derived from the conversion of glycolic acid ester and the selectivity to glyoxylic acid ester is not sufficiently high. Further, it may be a problem that the feed of gas flow required is large, the preparation of catalyst requires complicated pre-treatment, and the reaction system requires installation of a pre-heating apparatus prior to the reactor.
Bull. Chem. Soc. Jpn., 66, 1542(1993) describes a process for preparing ethyl pyruvate from ethyl lactate using an oxide of Mo, Fe, Sn, Bi, Te, Ti, or Zr. However, the indicated yields of ethyl pyruvate, that is, 80% or less, are not satisfactory.